Trends suggest industrialized world may be hitting peak travel

Analysis of recent trends in transportation suggest that the population of …

Transit, primarily in the form of automobile use, continues to be one of the biggest factors in the world's energy use. Although many vehicles have become dramatically more energy efficient over the last few decades, competing trends such as increases in the total miles traveled, have kept the total energy use rising. A study released recently, however, suggests that several industrialized countries have reached the point where their total transit use appears to be flattening out, an event the authors refer to as "peak travel."

The work was based on what seems to be an obvious contradiction: many economic and energy models assume that the rapid expansion of transportation will continue unabated for something approaching the indefinite future. But, realistically, transit faces some real limits. Some countries already have more cars than licensed drivers, many people aren't willing to spend much more of their days in transit, and the congestion and parking problems faced by urban populations can put a hard limit on automobile use. Population growth could drive a continued expansion, but that's also slowing in many industrialized countries, and their aging populations are expected to drive less.

So, the authors argue that saturation of a populations' ability and desire to travel may be closer than these models assume. And, based on recent data, they argue that it may be possible that we're already there.

As with most energy use analyses, the study requires a lot of data, not all of which is available for all the countries involved (in this case, the US, Canada, Sweden, France, Germany, the United Kingdom, Japan, and Australia). The authors therefore rely on a mix of interpolation and estimation to fill in some of the blanks; they skip pre-unification Germany entirely. All of the air travel figures come from domestic flights only.

What they find is that, prior to recent years, two forms of transit have driven most of the growth in miles travelled, and thus energy use: air and car travel. And, although air travel has continued to increase, car travel has started to decline (a trend that predates the oil price shock of recent years). As a result, since 2003, total miles travelled have flattened out and has started to decline in some countries. This flattening out is even more apparent when graphed against per-capita GDP. Here, most countries show a flattening out once they hit a per-capita GDP of $25,000 (in the US, the figure is $35,000, while Sweden shows a continuing rise).

There are lots of individual features hidden within these general trends. For example, the US drop in the energy intensity of car travel stalled once milage standards languished in the 1990s. In contrast, European countries started raising their gasoline taxes around the same time, and experienced the opposite trend. Longer flights are also less energy intensive, which means that domestic air travel is less energy-intensive in nations like the Australia, Canada, and the US simply as a function of geography.

Nevertheless, the authors argue that the GDP-related trends, which are more consistent across countries, suggest that there might be some common factors underlying the decline in travel, such as urbanization, increased taxes, aging populations, a saturation of automobile ownership, and a basic desire not to spend any more time behind the wheel. Carpooling has also seemed to decline to the point where it probably won't go down much further.

The authors also expect that any downward trend might accelerate. The rapid rise in oil prices that started in 2007 cut into vehicle travel, but only towards the end of their study period. An increased focus on less energy-intensive vehicles is also being matched by technologies like hybrid and plug-in vehicles, which may send the energy intensity of automobile transit in these nations even lower. If this turns out to be the case, then these countries may actually have reached peak transit, at least when it comes to energy use and CO2 emissions.

Beyond that, however, the authors say, "we do not make any predictions about future trends." Domestic air travel could expand more rapidly, or countries could begin major investments in road infrastructure, which could lure more drivers onto the roads, making this period of stability a temporary blip. (At the moment, neither of these appear especially likely to us.) In the end, the authors conclude, "The most fundamental point, however, is that continued, steady growth in travel demand cannot be relied upon."

The big caveat there is that these trends are occurring in the most developed economies. Places like Brazil, India, and China are only at the early stages of their domestic transportation booms. However, the trends identified by the authors suggest that these other nations won't experience a direct repeat of the experience of the countries analyzed here. Expensive oil and access to less energy-intensive vehicles will both be constant backdrops for their transportation booms, which may lead to a variety of different policy and consumer decisions.

Nevertheless, even if these nations experience a fraction of the transit growth that the US has, their impact on global carbon emissions could be enormous. The authors cite a study that calculated what would have to change in the US transit system in order to achieve a reduction proportionate to its global impact that's appropriate for reaching the goal of stabilizing the atmosphere at 450 parts-per-million of CO2. The list included several completely unrealistic options: fuel economy rising to 136mpg, biofuels reaching an 83 percent market share, or vehicle travel dropping by half. Hopefully, a combination of all of these will require less drastic efforts.